Refrigeration



Dec 25, 1928.

C. C. VAN NUYS REFRIGERATION Filed March 14, 1925 i i l i'hi INVENTOR BY32 am; 1122mm;

w ATTORNEYS Patentedbee. 25, 1928.

UNITED STATES PATENT OFFICE.

CLAUDE C. VAN NU YS, 0F CRANFORD, NEW JERSEY, .ASSIGNOR TO AIR REDUCTIONCOMPANY,-INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

REFRIGERATION.

Application filed March 14, 1925. Serial No. 15,486.

This invention relates to refrigeration involving the expansion ofcompressed gases with external Work to produce low temperatures, andparticularly to the useful recovery of a portion of the energy expendedin compressing the gases before expansion. It has a special advantagewhen applied in connection with a turbine in which the gases areexpandcd though it may also be used with expanders of the reciprocatingtype.

In existing liquefaction systems such as are employed in the separationof the constituents of the atmosphere for commercial purposes, expansionengines are used. It has been proposed to directly connect the expansionengine with the main compressor and thus to utilize the energyrecovered. The suggestion is wholly impracticable because it wouldrequire the expansion engine to operate at invariable speed whereas thevolume and pressure of the working fluid vary in different phases of theoperation. This requires a variation of the speed of the expander tomaintain efliciency, particularly in the case of turbine expansion sincethe turbine is efiicient only when operated at a definite speed with anygiven conditions of ressure and volume of the working fluid. onsequentlythe en ergy is usually employed in operating a direct current generator,and the current produced is dissipated through a resistance of the gridtype and is a total loss.

The installation of systems of greater capacity than those now in usewill depend to a large extent upon the possibility of recovering aportion of the energy derived from exansion in an economically usefulform.

imitations of speed of the expanding means must be avoided, andpreferably the energy should be recovered as electric current of thekind which is utilized in driving the motor for the compressor.

It is the object of the invention to provide for the conversion of theenergy derived from expansion and to automatically deliver theelectrical energy recovered to the power line and to permit adjustmentof the converter from time to time depending upon the existingconditions so that expansion at maximum efliciency is continuallyassured.

Other objects and advantages of the invention will be apparent as it isbetter understood by reference to the following specification andaccompanying drawing which illustrates diagrammatically the applicationof the invention to a liquefaction system.

It is assumed that the motor which drives the comprcssor will beoperated with alternatmg current of the kind usually supplied by powerlines. An ordinary alternating current synchronous generator could beconnected to the expansion engine or turbine, but the speed of operationof such a generator is necessarily invariable. There is no advantage,therefore, over the proposal to connect the expander directly to thecompressor. The difficulty is entirely avoided, however, by the use ofan induction generator iiith a wound rotor and a variable externalresistance connected therewith. Such a generator has the advantage thatthe speed and the' amount of energy transformed may be variedindependently within certain limits by varymg the resistance of therotor circuit. The operation of the generator may be regulated,therefore, depending upon the conditions of pressure and volume ofworking fluid in the liquefaction system to permit operation of theexpansion engine and particularly of a turbine at maximum efliciency.Thus, if the conditions of pressure and volume of working fluid requirethe operation of the turbine at a certain definite and previouslyascertained speed, the resistance connected to the rotor circuit of thegenerator will be adjusted correspondingly to permit operation of theturbine and generator at that speed while generating current which hasthe characteristics of the power line current and can be delivereddirectly to the power line.

The induction generator has another advantage inasmuch as it operatesinterchangeably as a generator or motor depending upon whethermechanical or electrical energy is delivered thereto. Consequently, aslong as the expansion engine or turbine delivers energy to thegenerator, power will flow therefrom to the power line. If the expansionengine or turbine fails for any reason to deliver energy to thegenerator the latter will act as a motor drawing current from the powerline and driving the expansion engine or turbine until the normalcondition is again resumed. The generator acts thus as a balance wheelto maintain the engine or turbine in operation at its speed of maximumefficiency under the. conditions which are assumed to exist regardlessof any temporary alterations of these conditions. Any permanent changein conditions is met by an adjustment of the resistance of the rotorcircuit which automatically changes the speed of operation of thegenerator and of the expansion engine or turbine to which it isconnected.

In carrying out the invention the expansion engine or turbine ispreferably directly connected to the induction generator which iselectrically connected in a shunt circuit from the power line feedingthe main driving motor for the compressor. The variable -resistance ofthe induction generator rotor is conveniently arranged so that it may bevaried at Wlll with the changes of conditions of pressure and volume ofthe working fluid. By suitable regulation of the generator the recoveryof energy at maximum efliciency 'is assured and the recovered energy isdelivered directly to the power line and utilized. The saving in energyis at once apparent as a reduction of the total energy consumed incompressing the gases prior to expansion thereof.

In the following more detailed description of the invention it isassumed to be applied to a liquefaction system whereby the constituentsof gaseous mixtures may be separated. It has, however, a broaderapplication to refrigeration where low temperatures are attained by theexpansion of a working fluid in an engine or turbine. The simple type ofliquefaction apparatus is described merely that the invention may beclearly explained.

Referring to the drawing, 5 indicates a column having compartments 6 and7 separated by a partition 8. A plurality of tubes 9 are supported inthe compartment 7 and communicate at one end with the compartment 6 andat the other end with a head 10. A plurality of trays 11 are disposed inthe compartment 7 to collect the liquid produced as hereinafterdescribed.

The compressed gaseous mixture enters the compartment 6 through a pipe12 and passes upwardly through the tubes 9 in indirect contact with theliquid in the trays 11. The resulting heat-interchange causes a partialliquefaction of the gaseous mixture in the tubes and the liquid thusformed flows downwardly through the tubes into the compartment 6. Inaccordance with the well-established principles of backward return inselective liquefaction, the liquid entering the compartment 6 from thetubes 9 is enriched in the more readily condensable constituent thereofwhile a residual gas consisting principally of the less condensableconstituent escapes to the head 10 and thence through a pipe 18.

Additional liquid to make up for heat losses in the column is suppliedto the compartment 6 through a pipe 13 which is controlled by a valve 14from a liquefier 15. The liquids combining in the compartment 6 aredelivered therefrom to a pipe 15 and pressure-reducing valve 16 to thetop of the column' 5. The liquid fills the trays 11 and flows downwardlythrough the column. As a result of the heat-interchange between theliquid and the gaseous mixture in the tubes 9, a portion of the liquidis vaporized and rises through the column from which it escapes througha. pipe 17.

The gases delivered through the pipes 17 and 18 are utilized in theliquefier 15 to secure by heat-interchange the liquefaction of a portionof the incoming gaseous mixture, the liquid formed being deliveredthrough the pipe 13 as hereinbefore described. The liquefier consistspreferably of a shell with a plurality of tubes 19 extendingtherethrough and communicating with compartments 20, 21 and 22 atopposite ends thereof. The pipes 17 and 18 communicate with thecompartments 20 and 22 at oneend of the liquefier so that the gases passthrough the communicating tubes and are delivered to the correspondingchambers 20 and 22 at the opposite end of the liquefier. Fromthe-chamber 22 the gases are delivered through a pipe 23 to an expansionengine, or turbine 24 under control of a valve 25. After expansion thegases pass through a pipe 26 to the chamber 21 at one end of theliquefier and thence through the communicating tubes 19 to thecorrespronding chamber 21 at the opposite end of the liquefier. From thechambers 20 and 21 the gases which are still at relatively lowtemperature are delivered through pipes 27 and 28 to an exchanger 29which is utilized to heat the incoming gaseous mixture.

The mixture is compressed in a compressor or blower 30 which is drivenpreferably by an electric motor 31. The motor is supplied withelectrical energy usually of the three phase alternating type through apower line 32. The compressed gaseous mixture passes from the compressor30 through a pipe 33 and water cooler 33 to the exchanger 29 where it.passes about bafiies 34 in contact with tubes 35 and 36 through whichthe gases are delivered from chambers 37 and 38. These chambers areconnected to the pipes 27 and 28. The tubes 35 and 36 communicate withchambers 39 and 40 at the opposite end of the exchanger having outlets41 and 42 through which the gases are discharged to the atmosphere ordelivered to suitable receptacles therefor.

In passing through the exchanger the incoming compressed gas is cooledby heat-interchange with the outgoing constituents from the column andin its relatively cold condition is delivered to a pipe 43. A branchpipe 44 delivers a portion of the cold gas under its initial pressure tothe liquefier where it is liquefied by indirect contact with the coldgases in the tubes 19, and it is finally delivered through a pipe 13 tothe chamber 6 of the column. The balance ofthe gas pames through III apipe 45 controlled by a valve 46 to an expansion engine or turbine 47where it is expanded with external work. The cold gas from the engine orturbine is delivered through the pipe 12 as hereinbefore described tothe chamber 6 of the column.

As the result of the operation under properly regulated conditionsliquid enriched in oxygen, for example, accumulates in the chamber 6 andis delivered through the pipe 15 and expansion valve 16 to the upperpart of the column. It descends through the trays 11 therein and isvaporized by heat-interchange With the gas in the tubes 9: The vaporescaping through the pipe 17 is the gaseous mixture enriched in one ofthe constitu- GIIi/S for example, oxygen, which is one of the ofsimplicity and economy.

he engines or turbines 24.- and 47 are connected either directly orthrough belts or other driving means to induction generators 48 and 49.having field windings 50 and 51. The rotor circuits of the generatorsare connected through brushes 52 and 53 to variable resistances 54 and55. Suitable means for varying the resistances are provided as is usualin such apparatus. The field windings are connected by conductors 56 and57 in parallel with the power lines 32. The generators are designed todeliver current having the same characteristics as that of the powerlines 32, and consequently the application of power to the generatorswill result in the delivery of current to the power lines and thecurrent will be utilized in the motor 31.

As hereinbefore indicated, the system is particularly advantageous inconnection with the use of turbines for expansion since turbines operatemost efiiciently only within a limited range of speed for any givenpressure and volume of gas. The provision of variable resistance in therotors of the generators permits the regulation of the generators toproduce current of the desired characteristic at a speed of o rationwhich is determined by the moste ective speed of the turbines.Consequently the pressure and volume of the gas being known, the turbinecan be operated at the most efiicient speed and the energy deliveredthereby can be converted directly into current which is reused indriving the compressor. Leaving out of account the losses due tomechanical and electrical inefliciency,

therefore, the energy required to operate the system is limited to therequirement for separation of the gaseous constituents plus the lossesresulting from heat-leakage. The generators act, moreover, to maintainthe system in its normally efficient operating condition during anytemporary failure of the ressure and Volume of the expanding gases causeat such times the generators will act as motors drawing current from thepower line and driving the turbines at their proper speed for eflicientoperation. If the unusual condition continues a new adjustment must bemade, but if it is only temporary the resumption of normal conditionsresults in the generation of current which is returned to the powerline. This condition assures maximum efficiency of the system.

The invention depends upon and .comprehends the utilization of electricgenerators capable of producing current of predetermined characteristicsunder variable speed conditions so that the energy recovered can betransformed and utilized directly and without unusual loss in thesystem. While it would be desirable in a liquefaction system to limitthe input of energy to that required for the separation of theconstituents and for losses unavoidable in the system, practicalconsiderations require the application of a considerable additionalquantity of energy. The recovery of a portion of the energy input isaccomplished most effectively in the manner hereinbefore described.

Various changes may be made in the form and arrangement of the parts, itbeing understood that no attempt has been made to illustrate anddescribe herein details of liquefaction systems which are known to thoseskilled in the art.

I claim:

1. A method of refrigeration, which comprises compressing a. gas withexpenditure of electrical power from an external source, cooling andexpanding the gas to recover energy therefrom, thereby further reducingthe temperature of the gas, converting the recovered energy intoelectrical power having the same characteristics as the power which isutilized in compressing the gas, supplementing the external. power withthe power thus developed, and regulating the rate and degree ofexpansion by adjusting the conversion to produce the desired electricalcurrent while expansion is conducted at maximum efficiency under givenconditions of pressure and volume of the gas.

2. A method of refrigeration, which comprises compressing a gas withexpenditure of electrical power from an external source, cooling andexpanding the gas to recover energy therefrom, thereby further reducingthe temperature of the gas, converting the recovered energy intoelectrical power having the same characteristics as the power which iscoolin and expanding the gas to recover energy t erefrom, utilizing theenergy to enerate electrical power having the same 0 aracteristics asthe power which is utilized in compressing the gas, flexibly associatingthe two power sources to supplement each other, and regulating the rateof expansion by adjusting electric variables to ermit expansion atmaximum efliciency un er given conditions of pressure and volume of thegas.

In testimony whereof I aflix my signature.

CLAUDE G. VAN NUYS.

